fix(Build): Allow Cordio to Build with Custom BSPs

[EricB-ADI]

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Description

Cordio depends on led.h and led.c, which required board.h and board.c. If LIB_BOARD=0 cordio fails to build. This is an issue with custom boards not in the MSDK. cordio.mk now uses BOARD_DIR directly to allow this to override the LIB_BOARD switch.

[Jake-Carter]

@EricB-ADI @kevin-gillespie LIB_BOARD=0 isn't intended as the mechanism for implementing custom BSPs. It disables the BSP abstraction entirely (which Cordio is dependent on for the HAL).

Custom BSPs should use the existing options to provide a "board.h", so I think adding BSP_SEARCH_DIR to CFG_DEV here would be sufficient to get them working.

Supporting LIB_BOARD=0 would mean supporting a build without the concept of a BSP which implies no "board.h". We could check for the LIB_BOARD definition to wrap the inclusion. It gets added here:

msdk/Libraries/libs.mk

Line 35 in bb1f929

PROJ_CFLAGS += -DLIB_BOARD

diff --git a/Libraries/Cordio/platform/targets/maxim/max32655/sources/pal_uart.c b/Libraries/Cordio/platform/targets/maxim/max32655/sources/pal_uart.c
index 16dd4dd44a..635dfb725d 100644
--- a/Libraries/Cordio/platform/targets/maxim/max32655/sources/pal_uart.c
+++ b/Libraries/Cordio/platform/targets/maxim/max32655/sources/pal_uart.c
@@ -35,7 +35,9 @@
 #include "pal_led.h"
 #include "pal_sys.h"
 
+#ifdef LIB_BOARD
 #include "board.h"
+#endif
 
 #include "uart.h"
 #include "sema.h"
diff --git a/Libraries/MiscDrivers/LED/led.h b/Libraries/MiscDrivers/LED/led.h
index 6ea14a3362..a3353123c9 100644
--- a/Libraries/MiscDrivers/LED/led.h
+++ b/Libraries/MiscDrivers/LED/led.h
@@ -27,7 +27,9 @@
 #define LIBRARIES_MISCDRIVERS_LED_LED_H_
 
 #include "mxc_assert.h"
+#ifdef LIB_BOARD
 #include "board.h"
+#endif
 #include "gpio.h"
 
 #ifdef __cplusplus

... but the build error moves to missing definitions on TERMINAL_UART, etc.

"board.h" seems the only mechanism for users to pass these in to the HAL, so this may not even be useful.

[EricB-ADI]

@Jake-Carter I updated it and it seems to be working. You are good to review

[Jake-Carter]

Thanks @EricB-ADI

I caught a couple edge cases. It seems like the most consistent way to do this is to export BOARD and BSP_SEARCH_DIR. exports in general should be used sparingly but in this case I don't see a need to build a library with a different BSP than the app code.

Then, the recursive build call needs to include board.mk in its internals. I re-leveraged libs.mk again for this. In my testing this gets the Cordio lib and app code builds synced up and using the same custom BSP. It's also more consistent with the direction I'd like to move for libraries in general, like for what we did with TinyUSB (#1101).